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Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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333 FXUS61 KPBZ 151157 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 757 AM EDT Thu Aug 15 2024 .SYNOPSIS... Dry and comfortable again today with warmer temperatures. A low pressure system will begin to slowly cross the Great Lakes region Friday and drift eastward into early next week. This pattern will bring with it the risk for periodic showers and storms. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... KEY MESSAGES: - Dry weather continues today with warmer temperatures. ------------------------------------------------------------------- Rising heights at 500mbs, and high pressure at the surface, will provide another dry day with plenty of sunshine. Warm air advection, within the eastward moving ridge, will nudge temperatures a few degrees above normal. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... KEY MESSAGES: - Shower/storm chances increase Friday, but timing issues still remain. - The threat for rain continues into Saturday with the slow passage of a surface front. ------------------------------------------------------------------- A large upper level low will drift toward the western Great Lakes on Friday. Waves of energy, rotating around the low, will be ejected eastward, crossing the region on Friday. The first wave in the morning will use up most of its energy breaking down the ridge axis which will be located over western PA. This will bring an increase in cloud cover, but should limit the rainfall. A second and stronger wave will cross Friday afternoon, pulling a surface front through the area. This will provide a higher risk for widespread shower activity. The convective threat is still murky due to a lack of instability and strong shear. Latest NBM data shows CAPE values less than 1000 j/kg, with much of the deterministic model data advertising wind shear of less than 20kts. An additional hindrance to storm development would be the increased cloud cover Friday morning as well as the warm air advection aloft. Latest CAM models are showing a line of storms moving across western and central OH Friday morning, but then weakening as they move further eastward. The CAMs are also hinting at the morning convection diving southward into a region of higher instability and stronger shear. The NBM keeps the higher probability for thunder later in the day with a large chunk of those higher numbers over Ohio. PWAT values will rapidly increase Friday, so if stronger convection does develop, there will be the threat for heavy rainfall. Temperatures Friday will cool a bit, closer to seasonal averages. The 500mb low will continue to drift eastward on Saturday, lowering heights even further over the region. A surface cold front, extending south of the stacked system, will cross the area Saturday afternoon. The risk for showers and storms will continue Saturday, but still much to be determined. NBM is showing a more buoyant atmosphere and deterministic models are increasing the shear to around 30kts. So if storms can initiate the ingredients will be in place to support stronger convection. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... KEY MESSAGES: - Ensembles favor Great Lakes troughing into early next week that would maintain low probability, diurnally driven convection. ------------------------------------------------------------------- Upper trough crawls east across western and central PA on Sunday, with shower chances continuing especially over PA/WV counties. Ensembles indicate that long wave trough will continue to linger in the Great Lakes and Northeast States Monday, Tuesday, and Wednesday. The standard deviation of 500 mb heights in this area gradually increase with time as the details of short wave troughs become less and less evident. NBM provides low rain chances during the period with somewhat higher values on Monday, but confidence is low and it certainly could end up being dry for a few days with northwest flow. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... After river valley fog diminishes by mid morning, high pressure will maintain dry conditions today. Dry weather will continue overnight with a lowering VFR cloud deck in advance of shortwave troughing. .Outlook... VFR conditions are expected to continue into early Friday morning before a shortwave brings chances of rain showers and thunderstorms to the area. Probabilities of MVFR are around 10%-20% on Friday for all sites due to lowering VIS. An upper level trough moves through on Saturday, causing showers and occasional thunderstorms. MVFR (50%-70%) and IFR (30%-50%) restrictions caused by low CIGs are more likely Saturday morning, but could remain through the afternoon. Periodic showers and thunderstorms with occasional restrictions are possible through Monday with the slow moving trough. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...22 NEAR TERM...22/Shallenberger SHORT TERM...22 LONG TERM...Craven AVIATION...Rackley/88